Ultrasound is the principal method used for diagnosing deep venous thrombosis in the United States, and its accuracy and limitations are well known. As venous ultrasound examination has matured, several controversial issues, primarily clinical, have arisen concerning the application of this diagnostic method. This article addresses some of the more noteworthy and vexing issues, including, but not limited to (a) the need to examine both legs in patients with unilateral symptoms; (b) the role of venous ultrasound in patients with bilateral leg swelling; (c) the necessary extent of the venous ultrasound examination; (d) the importance of calf vein thrombosis; (e) the significance of negative leg veins in a patient with possible pulmonary embolus; and (f) deep venous thrombosis in patients with occult malignancy. Technical aspects of the venous ultrasound examination, and diagnostic accuracy are not described.